One box cars and the like are designed not only to accommodate occupants but also to load cargo, so that an average number of seats and a cargo space are provided. Additionally, in many cases, seats other than a driver's seat and a front passenger's seat are made up of detachable seats or movable seats. Then, when there is much cargo to be loaded in the vehicle, the detachable seat or seats are detached or the movable seat or seats are moved to ensure a loading space for the cargo.
In the case of the detachable seat or the movable seat, a hinge hole is provided in an end of a rail which supports the seat, while a latch is attached to the other end of the rail. Then, one end portion of the rail is mounted so that a hinge shaft which is provided on a surface of a floor is rotatably supported in the hinge hole, whereby the detachable seat or the movable seat can be rotationally moved around the hinge shaft. On the other hand, with the detachable seat or the movable seat allowed to rotationally move around the hinge shaft, the latch attached to the other end of the rail is brought into engagement with a striker which is provided on the floor surface, whereby the detachable seat or the movable seat can be fixed to the floor surface.
Incidentally, when a distance between the hinge shaft and the striker is shorter or longer than a reference distance due to a mounting error of the hinge shaft or the striker or the like, the latch is not allowed to engage with the striker, and therefore, the detachable seat or the movable seat cannot be fixed to the floor surface.